Low gloss powder coatings are needed in industries such as the automotive and furniture industries. Traditionally, the gloss is reduced by the formation of a minute surface texture, which scatters the light at the coating surface. In doing so, additives or fillers are incorporated into the coating composition to form minute surface irregularities. However, gloss reduction through incorporating additives or fillers often sacrifices physical properties of the cured coating. Compounding into a powder coating composition two components exhibiting different curing reaction rates can also reduce the gloss of the cured coating. However, this way of reducing gloss is limited to certain powder compositions since it is dependent on specific resins and curatives, and gloss is sensitive to heating rates.
Some low gloss coating compositions have been proposed. For example, U.S. Pat. No. 6,093,774 describes a low gloss powder coating composition comprising a glycidyl-containing acrylic polymer, and two acid functional crosslinkers.
U.S. Pat. No. 5,744,522 discloses a low gloss coating composition comprising a glycidyl group containing acrylic copolymer; an aromatic polyester containing carboxyl groups; and an isocyanurate curing agent.
U.S. Pat. No. 5,684,067 discloses a low gloss coating powder composition comprising polyester resin; triglycidyl isocyanurate (TGIC); a copolymer of ethylene and acrylic and/or methacrylic acid; a compound selected from 2-mercapto benzothiazole and metal salts of 2-mercapto benzothiazole.
U.S. Pat. No. 5,491,202 discloses a low gloss powder coating comprising three thermosetting polyester resins and a hardener, e.g., glycidyl compound, amide compound, blocked isocyanate compound, etc.
U.S. Pat. No. 5,436,311 discloses a matte powder coating composition comprising a mixture of a linear carboxyl polyester and glycidyl acrylic copolymer.
Other low gloss coating compositions are proposed in U.S. Pat. No. 4,419,495 and U.S. Pat. No. 4,242,253.
In spite of all the efforts made to reduce the gloss, it has been difficult to lower the gloss of the epoxy functional acrylic powder coatings without sacrificing considerable physical properties, or compromising appearance.